Convertible crawler shovels and like machines



June 28, 196.0 c. c. LANGs'rRoTH CONVERTIBLE CRAWLER SHOVELS A'ND LIKE MACHINES Filed March 14, 1957 3 Sheets-Sheet 1 avaiA unfri,

/NveNroR IC l/vssmoru iff-orner s June 28, 1960 c. c. LANGsTRoTH 2,942,559

CONVERTIBLE CRAWLER SHOVELS AND LIKE MACHINES Filed March 14, 1957 5 Sheets-Sheet 2 /NvsuroR C l 0//6 afnam June 28, 1960 c. c. LANGs'rRoTH 2,942,559

CONVERTIBLE cRAwLER sHovELs AND' LIKE MACHINES Filed March 14 1957 3 Sheets-Sheet 3 m E R mmlllnollolbloj. lllnwllmmllqol l- 1 i 2,942,555 Patented VJune 28, y1960 United Statesv Patent Oce This invention relates to power shovels and like machines and particularly to meansfor converting such power shovel on whichthe travellingvgear can be quickly and efficiently exchanged fromy Crawler .tre'adnt spool wheelktype without theuse of built'inextensionfo retac- Y' Y' Y tion outrigge'r gear. A further object' of the invention toy provide vertible power shovel particularlysuitedv ,to'opera e on or machines from crawler tread operation to spool wheel operation and the converse.

Power shovels generally follow awell established design insofar as their main operating characteristics are concerned and are provided with travelling 'gear to suit the work for which they are primarily built.4 However, it o ftenloccurs that an operator has work to, be done by the power shovel which requires that the shovel be equipped with crawler treads for working on the ground and for other work requiring the shovel to be equ'ippedwith wheels for operating on rails. VThis is particularly'the case with railway opeartors where one f class fof work yis ditching along side the railroad tracksV where the power shovel can be operated from the tracksiandwhere other work beyond the normal reach of a powershovel'coniined to tracks necessitates the'use of a power shovel equipped with crawler treads.' 'Insuch circumstnces'the cost of providing separate shovels with diierent ftype 4trflds is considered too high and 'further, in most cases, it involves the use` of two at cars to transport the`zshovels to the work location. t

Power shovels'have been made convertible in thepast by providing a main travelling gear of -either the crawler t or wheel type and having an auxiliary travellirlggearv of the alternate type to the main gear, this auxiliary travelling gear usually being controlled by displacement mechanism, displacing one travelling gear vertically with relation' to the other, orthe displacement mechanism may'operate some form of out-rigger gear .to swing the' auxiliary travel-v ling gear up and out from the; machine. Such 'combinaf ing the 1 na in` r crawlentread'."

tions of main andv auxiliary travelling gear are generally i considered impracticable particularly for railroad -Work where the machinev has to be transferred on and olf au railroad atcar.

The present invention consists essentially in providing, in a;power shovel, a main truck frame capableof taking either crawler tread or wheel travelling gear, the 'alternative forms oftravelling geartbeingr arranged to ht into thel same forked endsof the side members lof theffniain frame and' to be aligned on the 'same centres. "The conversion of the machine froml wheel to crawler tread travelling and conversely Ibein-g carried out on a railroad atcar provided with a set of rails and crawler'V tread "supl.

wheelsll;

porting timbers laid parallelwith and on b'othlsides of the rails and whose top surface is ush with the top of the rail to enable the crawler treadZ to be maneuvered-into place and be tted to the machine without interference from the rails. Both the wheel assembly and the crawler track assembly being equipped with similar driving and nomdriving shaft assemblies which lit into the-y s'arneV Y forked ends of the machine side frames and are tensioned similarly. The alternative gear not in use is storedy on the top of the atcar betweenlthe rails and can 4be manen-J vered thereonby connecting'thepa-rts by slingsor cables to the forks'of the shovel dipper.

The object of the invention is therefore to'provide a treadidlr'wheelsniounted thereon.A

A twoI side 'memberslzm "and'sutablefdrnemb Y The Asidemembers arefcompo'sed of vay pairoflreintorecd oifv a railroad atcar with either crawler tread fon-'spool I tread or wheel shaft assemblies and to hold these shaft assemblies to auniforin distancebetwnc'entres, A further object of ythe invention is to provide a railroad flat car having rail andjtread surfaces of uniforni" height providing" working surfaces upon which thev wheels or crawler treads of a powerfshovel canbese't'for quickV replacement with each other. Y These and other objects lof the inventionl'will: heapparent from thefollo'wng speciiicatiron" and the drawings attached thereto which.: Y Fig. l is a side yelevation showingin outline, afpowe'r Y shovel mounted on a railroad flatcar and 4showinga crawller tread in place under the side frame of thepower shovel andhattachedlt the' shovel member for maneuvering into'place preparatory to fitting `the tread over'the idler Wheels'ofthe truck'frame. xFig' 2;' is a partial plan'view of one side of sh c vel k mainframe Vfitted withI poolwheels an f portedfon jrailskjon a Irailroad iiajt'caran' driving Vgeary shaftla", Vmbly 4in section -fV Figg 3is 'a s ide view/"of Y Fig, 4 is a driving enana-wbr meenam-angliae Eigsgzjand Fig. 5 is a partialvplan view silrlilartoY Fig.

rame'of thev pow rshovel 'equip 'e Eig. 6 is a side viewfoi" the'power shovel maii fr ai'nefV side member ttedwith the crawler treadshown in;

Fig. 7v is: afd'rving end view l ofthe assembly'sho Figs. 5 and 6', with' theframe raisedto allowth v to be drawn in toposition. i g Y Fig. '8 is a horizontal section of the` non-'driving end ol"y the 'truck assemblytaken A`on the line' 81E-8 ofFig." i

"Fig, Vis av diagram showirigawdrive applic wheels "at bothends'ofthe shovel."I j Referring'to the drawings, the `power'shove l"5w's sho surfaceftth'e rails sjjan'd are spacedout'wardl rail f8` tn provideclearanc'e forzthfrirn" flfhepower shovel'S-herenafter describedinde prima ,fr use in; fairrpad work "alribe-'jieasily `ccinrrertille' ffromrail to' iraw' converse. HThe frameof the-power shovel 5 consist fe" 'power shovelv niaiir ine Heirwith a channelvmemb'rs 14 set ba'cl'tdfbackfand apart 1 .l 1 g to provide clearance for the; spool wheels l tally at 16 to provide seats for the adjusting shaft bearing blocks 17, the -inner ends of the slots 16 being blocked off by the transverse webs' 18 extending vertically between the web and the top and bottom anges 14a and 14b of the side members 12. The shaft bearing blocks 17 are retained within thev slots 16 by the end keeper plates 19 and are held in horizontal adjustment by the adjusting screws 20 passing through the transverse webs 18. The adjusting screws 20, adjusting the position of the rotating driving axles 21 are anchored in the boss 22 and are locked in the adjusted position by the nuts 23 and 23a on either side of the transverse web 18 while the adjusting screws 20a holding the non-driving end shaft bearing blocks 17a are held by the single nut 24 which is anchored against rotation after the bearing adjustment has4 been set. Where the non-driving axle 25 carries a freely joui-nailed idler crawler tread sprocket as generally shown in Fig. 8, the sprocket 15a is journalled on the sleeve bearing 26 and it is preferable that the shaft `25 be non-rotative. In this case theadjusting screws a are passed through the bearing blocks 17a and the shaft 2.5.

The drive shaft 27 drivably connected with the main I drive of the power shovel 5, drives the sprocket 28 and through the drive chain 29 rotates the `sprocket 30 and the driving axle 21.

In order to obtain the maximum traction effect from the spool wheels 11 and 11a, the axles 21 may be joined together by the floating axle 21a while the axles 25 may be joined together by the oating axle 25a as shown in the diagram Fig. 9. In this case, instead of the drive chains 29 being connected to each of the axles 21, one drive chain is connected to one of the axles 21 while the other drive chain is connected to one of the axles 25, thereby applying traction to each of the wheels 11 and 11a. i. y j

A pair of idler wheels 31 are journalledin the bearings 32 on the top'ianges 14a of each truck frame side member 12 and carry the crawler tread 39, formed by the links 33, between the sprockets 15 and 15a above and clear of the truck side members 12.` ASimilar idler wheels 34 are journalled inthe bearings 35 on theffunderside of the bottom flanges 14b of the truck side members CII 12 to support the truck frame when the crawler treads are in use. Theidler wheels 31 and 34 are individually located between the pairs of spaced channel members 14 constituting the side members 12 ofthe truck 'frame and the lower idler wheels 34 are located vertically such that the lowest point of their rims aire slightly aboveV the top level of the rail 8 when the truck is fitted with the spool wheels`11 and 11a, as seen in Fig. 3.

It will be noted that the tread centre line A--A shown in Figs2 and 5, whether for spool wheel drive or crawler tread drive of the powerwshc'vel, remains in the same position, le., centered with the trails 8 and that the drive to the driving shaft also remains in the same location. The drive shaft assembly for the spool wheel drive consists of vthe axle 21 to whichis keyed a chain sprocket 30 and a spool wheel 411 and a pair of shaft bearing blocks W- 17 complete` with adjusting screws 20, while the 4substitute drive shaftA assembly for fthe crawler tread drive consists of the shaft 21 to which is keyed a chain sprocket30 and a tread sprocket 15 and a pair of shaftbearing blocks4 17 complete with adjusting; screws 20. Similarly the nondriving axle assembly for the spool wheel drive consists of the shaft 2,5, a journalled spool wheel 11a and rpair of shaft bearing blocks 17a complete with adjusting screws 20a, while the substitute non-driving shaft assembly for the crawler tread drive consists of the shaft 245, a journalled tread sprocket 15a and a pair of shaft bearing blocks 17a complete with adjusting screws 20a. f

` Thefabricated structuralsteel frame described, withzits spaced apart channel side members givingclearance for the wheels v11 and 11a and the tread sprockets 15 Aand 15d,

may be'replaced by a cast frame having suitable recesses to give clearance for the wheels and tread sprockets and also have suitable pockets for the adjustable shaft bearing blocks 17l and 17a.

Having described in detail the constructional features of the power shovel drive for either spool wheel drive or crawler tread drive, the method of converting the power shovel from one form of drive to the other, will now be described.

Presurning that the power shovel is fitted with spool wheels 11 and 11a aand running on fthe rails 8 on top of the atcar 6 with the crawler tread strands and substitute shaft assemblies stored on the top of the atcar. The order of conversion will be as follows:

Conversion of one side of the truck is completed before work is started on the other side of the truck. f

(1) Move the power shovel to the extreme end of the atcar 6 which will place the roller drive chain end of the truck frame 12 facing the stored crawler tread strands. The wheels 11 and 11a being blocked in this position by the wheel chocks 42. A

(2) Connect a sling 36 to the crawler tread link pin 37 which is nearest to the power shovel and hook the other end -of the sling 36 onto one ytooth ofthe shovel clipper 38.

(3) Liftthe crawler tread strand 39 as high as possible with the dipper 38 and swing the strand over and onto the top of the timbers 9 as much as possible. Lower the end ofthe strand 39 and remove the sling 36. Complete the lineup of the treads with the dipper 38 or by means of crowbars.

(4) Move the power shovel to within 18 inches of the crawler tread strands.

(5) Raise one side of the power shovel with the use of lifting jacks 40, placing one under each of the main cross members/13. The lifting jacks should be placed as near. as possible to the inner'of 'the timbers 9 without interfering withthe movement of the crawler treads thereong The power shovel should be raised just sufficiently to allow the crawler-tread strand to pass freely under the lower idler wheels 34.

(6) Remove the four end keeper plates 19 from the ends of the truck side frame.

(7) Open roller drive chain 29 and remove the chain from the chain sprocket 30.

(8) vRemove the nut 23a from the adjusting screws 20. The roller chain sprocket and spool Wheel shaft assemblies can now be removed from the slotted end of the truck side `members 12 by raid of slings attached to the dipper 38.`

(9) Swing the shovel dipper 38 around to the opposite end of the power shoveltruck and `remove the nondrive spool wheel` assembly'in the same manner as above described, except that the end locking plate 41 is removed from the adjusting screws 20d instead of a locknut 23a.

The dismantled spool wheel assemblies are now stored out of the way on the atcar. i

(10) Attach one end of a wire rope cable or'sling 36:7to the tread link pin 37 of the crawler tread stand 39 nearest to the ldrive-end of the` machine; pass it under and into the grooves of the lower idler wheels 34 andhitch .the other end of thecable` or sling 36 to thedipper 38, which is pointed outwardsv from the non-drive en d as shown-in Fig. 1. With` the aid of the hoisting andcrowding-out action of the dipper pulling on the cable 36 the crawler tread strand 39 is pulled along the timbers 9. .Place half the tread strand 39'less three tread links 33 out in front of the non-drive end and leave the remaining part under the idler wheels 34 with tread links 33 left v-for folding up and over purposes on the tread drive sprocket 15.

' (1l) Sling the complete tread drive and roller chain sprocket shaft assembly including adjusting blocks 17 and' screws 20. to thedipper 38. Lift and place the complete assembly on top of the tread strand 39 closef to the end of the truck side frame 12. Withv the shaft of the assembly held horizontally, roll the assembly on the treads and into the forked end of the side frame 12, at the same time guiding the adjusting screws 20 through the holes in the transverse webs 18.

(l2) Wrap the roller drive chain 29 around the outer,

halves of lboth chain sprockets 28 and 30 and join the chain ends.

' (13) Adjust the roller drive chain 29 gradually to its proper tension by turning both nuts 23, making su-re that the whole tread drive sprocket and shaft assembly is kept lined up parallel with the truck side frame '12. Finally lock the whole assembly in place with the lock nuts 23a.

(14) The two end covers 19 are now replaced on the forked ends of the truck side frame and securely fastened in place.

(15) The non-driving end idler sprocket shaft assembly is slung into place on top of the tread strand 39 close up to the non-drive end of the truck side Iframe 12. With the shaft held horizontally the assembly is rolled on the treads and into the forked end of the side frame 12 as far as it will go. Set the adjusting screws 20aY and nuts 24 in place, leaving all take-up on the adjusting screws to be made after the tread strand 39 has been completely assembled in place with ends joined.

(16) Replace the end covers 19 on the non-driving end. v

(17) Lower `the machine down on the crawler tread strand 39 by removing the-two lifting jacks. Fold the last three tread links 33 upV and over the tread drive sprocket 15 and attach .a cable to the pin 37 in the last tread link'. Pass the Vcable overthe grooves of theV top idler Wheels"31 and hitch the free end to the tooth'of the shovel clipper 38. With the machine set in travelling position and a constant tension on the cable, move the machine slowly vin the direction of the dipper 38.y This will draw the tread strand 39 over the tread idler sprocket la'and'top'idler Wheels 31. When the last two tread links`33 are in a position'to fold down over the tread idler'sprocket 15a, stop the ymachine and unhitch the cable. iThe Atwo end tread links 33 remaining on .the timbers 9 can now be raised and`joined to the other end of the tread strand lying over the top of the side frame.

(18) The' final adjust-ment of the tension on the crawler tread ,strand is made by gradually turning both nuts 24-on theadjusting screws 20a and taking up all unnecessary slack inthe tread strand, -making sure that thewhole tread idler sprocket shaft assembly is kept v 'parallel with the trunk side frame.

. The above procedure completes the conversion of .one side of the power shovel fromY spool wheel to crawler tread assembly. The procedure isirepeated for the other side of the machine by first moving the machine on the flatcar back to the startingpoint set out above in paragraph 1 of the conversion procedure are following the same procedure.' Y -f Q The power shovel when completely converted to crawler track assembly can be readily Ymoved oil the ilatcar for operation on the groundrby-the 'use of a ramp set against the atcar. j

V;1"l 1e opposite of the above procedure yis followed when the power shovel is returned to the flatcar and it is desired tor convert -back to spool wheel drive.

-At all times, lthe top surfaceof the atcar is ready equipped to take either a spool wheeled machine. or a crawler tread equipped. machine and during the process ofvconversion one sideof the machine may be equipped with spool wheels While the other side is equipped with a crawler tread, neither of which prevents the machine fromvbeing moved along the sur-face'of the atcar from one-position to another for the purpose of facilitating the fitting orremoval of the vari-ous parts ofthe machine movingelernents. The' rails 8 and the timbers9 I lbeing lushwith eachother allows the crawler tread to be moved freely intoposition under the side` framek of. the, machineand to'straddleftherail and be aligned i6 with the cent-re line of the drive and 4the rail, Ithe edges of the timbers 9 providing a ready check on the parallel alignment of the assembly. The shaft assemblies for both spool wheel and crawler tread operation are identical in their fitting into the forked end of the side frames and with the location on theirshafts of thechain drive sprockets therefore the substitution of one for the other presents no problem in fitting `or yalignment during the conversion operation. The tensioning of the lchain drive for wheel operation of the machine presents no problem except to make sure that the drive shaft assemblies hold the wheels parallel with each other. When crawler treads are to be fitted to the machine it is essential that the chain drives be tensioned before the crawler tread strands 39 are fitted and that the tread sprockets 15 are parallel with each other and aligned with the permanently fitted idler pulleys 31 and 34. The crawler tread strands 39 are tensioned at the .non-driving end of the machine without affecting the setting of the drive shaft assembly and tension. Y f

A- power shovel having its main frame equipped to take alternative shaft assemblies having wheels or crawler tread sprockets and lbeing permanently equipped with tread idler wheels, together with a railroad atcar having rails and crawler tread timbers, offers a solution to the conversion problem, which conversion can be carried out with accuracy and a minimum ofdelay. Further, Y

the conversion of the -machine can be carried out in the field only rwith the -use of equipment such as jacks and slings .that can be easily handled by vman power and the machine itself. WhatIclaimis: .1.'In a power shovel or like machine which is convertible between wheel and endless track traction, in combination, a main truck frame supporting the power shovel, lthe said main truck frame comprising a pair of side members tied .together in spaced relation, said side members being .formed of two `vertically disposed members assembled in spaced relation to each otherI to provide clearancey for the traction drive'elements of the l machine, a dn've shaft located-transversely between' said v side members, crawler tread idler Wheels journalled in said truck frame side members, a set of four wheel shaft assemblies including a traction wheel and a Apair of bearing blocks, a pair of sarid traction wheel assemblies including a drive member, a set of four crawler tread sprocket shaft assemblies including a` tread sprocket wheel and a pair of bearing blocks, a parir of said latter shaft assemblies including a drive member, said sets of sha-ft assemblies fitting into the ends* of said truck frame as alternative wheel or crawler tread traction members, the j said wheels and crawler tread sprockets being disposed".

between the spaced apart members of the said sideiframes in the same vertical plane as'V `the said crawler tread' idler wheels, drive means connecting thedrive members of said shaft assemblies .with the said drive shaft when, l

the said shaft assemblies are yiltted into vthe saidV truck frames, and a crawler tread fstrfand Vfitted over -said crawlerltread sprockets andidler wheels when the crawler tread sprocket shaft assemblies are tted truck side members.

2. In a power shovel or like. machine which is'convertible between wheel and endless track traction, in combination, a main truck frame supporting the power shovel,rthe said main truck frame comprising a pair of side members tied `together in spaced relation, said side members being of two vertically disposed membersV assembled in spaced relation to each other to provide clear-V to said main ance for the traction drive elements of the machine, a

drive shaft located transversely between 'the said side members, a pair of sprocket wheels on said drive shaft,

the said sprocket wheels being disposed one on the innerl side of each of said `truck frame side members, a pair' of sprocket rkdrive chains engaging with said Vpairjzof sprocket wheels, crawler tread. idler wheels journalled in said truck frame side members and having their lower periphery projecting below -the lower surface of said side members, a set of four wheel shaft assemblies including a traction wheel and a pair of bearing blocks, a parir of said wheel shaft assemblies including a drive chain sprocket wheel, a set of. four crawler tread sprocket shaft assemblies including a crawler tread sprocket wheel and a pair of bearing blocks, a pair of said latter shaft assemblies including a drive chain sprocket wheel, said sets of shaft assembliesv fitting into the ends of said truck frame as alternative wheel or crawler tread traction members, the said traction wheel and crawler tread sprockets being disposed between the spaced apart members of the said side frames in the same vertical plane as said crawler idler wheels, the said drive sprocket wheels of the said wheel shaft assemblies and of the said crawler tread sprocket shaft assemblies engaging with the said chain drives when the said assemblies are fitted -in the said truck frames, means to tension the said chain drives through their separate shaft assemblies, means to tension the non-driving shaft assemblies independently of the driving shaft assemblies, and a crawler tread strand fitted over said crawler tread sprockets and idler wheels when the crawler tread sprocket shaft assemblies are fitted to said main truck side members.

3. In a power shovel or like Vmachine which is conveit-ible between wheel and endless trackV traction, in combination, a main truck frame supporting the power shovel, the said main truck frame comprising a pair of side members tied together in spaced relation, said side members being formed of two vertically disposed Vmembers assembled in spaced relation to each other to provide clearance for the traction drive elements of the machine, a drive shaft located transversely between said side members, a pair of sprocket wheels on said drive shaft, the said sprocket wheels being disposed one on the inner side of each of said truck frame side members, a pair of sprocket chains engaging with said pair of sprocket wheels, crawler tread idler wheels journalled on the bottom surface of said truck frame side members, the said idler wheels being disposed in the central vertical plane of the truck side frames, a set of four wheel shaft assemblies including a traction wheel and a pair of bearing blocks, a pair of said wheel shaft assemblies including a drive chain sprocket wheel, a set of four crawler tread sprocket shaft assemblies including a crawlerV tread sprocket wheel and a pair of bearing blocks, a pair of said latter shaft assemblies including a drive chain sprocket wheel, said sets of shaft assemblies fitting into the ends of said truck frame as alternative wheel or crawler tread traction members, the said traction wheel and crawler tread sprockets being disposed between the spaced apart members of the said side frames in the same vertical plane as said crawler tread idler wheels, the said drive sprocket wheels of the saidwheel shaft assemblies and of the said crawler tread sprocket shaft assemblies engaging with the said chain drives when the said assemblies are fitted into said truck frames, means to tension the said chain drives through their separate shaft assemblies, means to tension the non-driving shaft assemblies independently of the driving shaft assemblies, and a crawler tread strand fitted over said crawler tread sprockets and idler wheels when the crawler tread sprocket shaft assemblies are tted in said main truck side members.

4. In a power shovel or like machine which is convertible between wheel and endless track traction, in combination, a main truck frame supporting the power shovel, the said main truck frame comprising a pair of side members tied togehter in spaced relation, said side members being formed of two vertically disposed members assembled in spaced relation to each other to provide clearance for the `traction drive elements of the machine, a drive shaft located transversely between said side members, a pair of sprocket wheels on said drive shaft, the said sprocket wheels being disposed one on the inner side of each of said truck frame side members, a pair of sprocket drive chains engaging with said pair of sprocket wheels, crawler tread idler wheels journalled in said truck frame side members, a set of four wheel shaft assemblies including a traction wheel and a pair of bearing blocks, a pair of said traction wheel assemblies including a drive chain sprocket wheel, a set of four crawler tread sprocket shaft assemblies including a tread sprocket wheel and a pair of bearing blocks, a pair of said latter shaft assemblies including a drive chain sprocket wheel, said sets of shaft assemblies fitting into the ends of said truck frame as alternative wheel or crawler tread traction members, the said wheels and crawler tread sprockets being disposed between the spaced apart members of the said side frames in the same vertical plane as said crawler tread idler wheels, the said drive sprocket wheels of the said wheel shaft assemblies and of the said crawler tread sprocket shaft assemblies engaging with the said chain drives when the said assemblies are fitted into the said truck frames, one of the pair of said wheel shaft assemblies which include the drive chain sprocket wheel being disposed in one side frame member at one end of the truck frame and the other of said pair being disposed in the other side frame member and at the opposite end of the truck frame, a oating axle connecting the pairs of wheel shaft assemblies at each end of said truck frame, means to tension the chain drives, and a crawler tread strand fitted over said crawler tread sprockets and idler wheels when the crawler tread sprocket shaft assemblies are titted to said main truck side members.

5. In a power shovel or like vmachine which is convertible between wheel and endless track traction, in combination, a main truck frame supporting the power shovel, the said main truck frame comprising a pair of side members tied together in spaced relation, saidside members being formed of two vertically disposed members assembled in spaced relation to each other to provide clearance for the traction drive elements of the machine, a drive shaft located transversely between said side members, a pair of sprocket wheels on said drive shaft, the said sprocket wheels being disposed one on the inner side of each of said truck frame side members, a pair of sprocket drive chains engaging with said pair of sprocket wheels, crawler tread idler wheels journalled in said truck frame side members and having their lower periphery projecting below the lower surface of the side members, a set of four wheel shaft assemblies including a traction wheel and a pair of bearing blocks, a pair of said wheel shaft assemblies including a drive chain sprocket wheel, a set of four crawler tread sprocket shaft assemblies including a crawler tread sprocket wheel and a pair of bearing blocks, a pair of said latter shaft assemblies including a drive chain sprocket wheel, said set of shaft assemblies including a drive chain sprocket wheel, said set of shaft assemblies fitting into the ends of said truck frame as alternative wheel or crawler tread traction members, the said traction wheels and crawler tread sprockets being disposed between the spaced apart members of the said side frames in the same vertical plane as said crawler tread idler wheels, the said drive sprocket wheels of the said wheel shaft assemblies and of the crawler tread sprocket shaft assemblies engaging with the said chain drives when the said assemblies are fitted into said truck frames, one of the pair of said wheel shaft assemblies which include the drive chain sprocket wheel being disposed in one side frame member at one end of the truck frame and the other of the said pair being disposed in the other s ide frame member and at the opposite end of the truck frame, a floating axle connecting the pair of wheel shaft assemblies at each end of said truck frame, means to tension the said chain drives through their separate shaft assemblies, means to tension the non-driving shaft assemblies of the crawler tread shaft assemblies independently of the driving shaft assemblies, and a crawler tread strand fitted over saidV crawler tread sprockets and idler wheels when the crawler tread sprocket shaft assemblies are tted to said main truck side members.

6. In a power shovel or like machine which is convertible between wheel and endless track traction, in combination, a main truck framesupporting the power shovel, said main truck frame comprising a pair of side members tied together in spaced relation, the said side members comprising vertically disposed pairs of channels spaced apart to provide clearance for the traction drive elements of the machine, a drive shaft located transversely between said side members, a pair of sprocket wheels on said drive shaft, the said sprocket wheels being disposed one on the inner side of each of said truck frame side members, a pair of sprocket drive chains engaging with said pair of sprocket wheels, crawler tread idler wheels journalled on the bottom surfaces of said truck frame side members, the said idler wheels being disposed in a vertical plane central between the pairs of channel members of the truck side frames, a set of four wheel shaft assemblies including a traction wheel and a pair of bearing blocks, a pair of said wheel shaft assemblies including a drive chain sprocket wheel, a set of four crawler tread sprocket shaft assemblies including a crawler tread sprocket wheel and a pair of bearing blocks, a pair of said latter shaft assemblies including a drive chain sprocket wheel, said sets of shaft assemblies fitting into the ends of said truck frame as alternative wheel or crawler tread traction members, the said wheels and crawler tread sprockets being disposed between the channel members of the side frames and in the same vertical plane as said crawler tread idler wheels, the said drive sprocket wheels of said wheel shaft assemblies and of the said crawler tread sprocket shaft assemblies engaging with the said chain drives when the said assemblies are tted into said truck frames, means to tension the said chain drives through their separate shaft assemblies, means to tension the non-driving shaft assemblies independently of the driving shaft assemblies, and a crawler tread strand tted over said crawler tread sprockets and idler wheels when the crawler tread sprocket shaft assemblies are tted to said main truck side members.

7. In a power shovel or like machine which is convertible between wheel and endless track traction, in combination, a main truck frame supporting the power shovel,

said main truck frame comprising a pair of side members tied together in spaced relation, the said side members sprocket drive chains engaging with said pair of sprocket Y wheels, crawler tread idler wheels journalled on the bottom surfaces of said truck frame side members, the said idler wheels being disposed in a vertical plane central between the pairs of channel members of the truck side frames and projecting below said frames, a set of four wheel shaft assemblies including a traction wheel and a pair of bearing blocks, a pair of said wheel shaft assemblies including a driven chain sprocket wheel, a set of four crawler tread sprocket shaft assemblies including a crawler tread sprocket wheel and a pair of bearing blocks, a pair of said latter shaft assemblies including a driven chain sprocket wheel, said set of shaft assemblies fitting into the ends of said truck frame as alternative wheel or crawler tread traction members, the said wheel and crawler tread sprockets being disposed between the channel members of the side frames and in the same vertical plane as said crawler tread idler wheels and connected to said sprocket drive chains through the said driven chain sprocket wheels, means to tension the said chain drives through their separate shaft assemblies, means to tension the non-driving shaft assemblies independently of the driving shaft assemblies, and a crawler tread strand fitted over said crawler tread sprockets and idler wheels when the crawler tread sprocket 'shaft assemblies are fitted to said main truck side members.

References Cited in the file of this patent UNITED STATES PATENTS 1,731,911 Sayers et al. Oct. 15, 1929 1,824,196 Cullen et a1 Sept. 22, 1931 2,311,304 Lehti et al Feb. 16, 1943 2,322,919 Burns et al June 29, 1943 2,344,764 

